Increased monitoring of environmental quality has resulted in a substantial rise in the number of identified sites of contaminated ground water. Accompanying this trend has been an increased effort to clean up these sites. In response, there is a need for improved below ground pumping systems to assist in these clean up efforts.
Ideally, below ground pumping systems used for these purposes will have a number of desired characteristics. Because of the large number of pumping systems required, it is desirable to minimize the cost of each pump and each installation. Accordingly, such pumps should be relatively simple and inexpensive and should fit in a small diameter well due to the increased cost of drilling large diameter wells. To minimize maintenance and repair costs, the pumps should have a minimum of moving parts and should have high reliability. Also, such pumps should be able to withstand corrosive fluid streams without failure.
Due to the possibility of exposure of the pumping systems to explosive gasses, pneumatic pumps are preferred over electrical pumps for pumping waste products. However, many of the currently used pneumatic pumps have a number of drawbacks. For example, many pumps in current use require external controlling devices which use timers to activate the pump on a fixed schedule. This necessity of external controllers adds considerably to the cost and complexity of the overall pumping system. In addition, the use of a fixed time pumping schedule has disadvantages since it may not result in pumping at the most opportune time to obtain the maximum production from the pump. For example, an external timer cannot sense variations in the flow rate of fluid into the pump and thus may result in either a too fast or a too slow pumping cycle.
There are pumps which avoid the necessity of external controllers by incorporating sensing means within the pump to detect when fluid has entered the pump to a desired level. Unfortunately, the prior art pumps which are capable of self activation have not proved satisfactory in many applications. One problem has been with the mechanical actuating and sensing mechanism within the pumps. Generally, such pumps use a float which rises when the pumps fills and lowers when the pump is empty. Actuating mechanisms which sense the movement of this float sometimes require considerable force to switch the pumps pneumatic vane on and off. This results in the necessity of a fairly large and heavy float which increases the overall size and cost of the pump system.
In addition to the problems with the actuating mechanism, the pneumatic valve used to control the flow of compressed air into these pumps have often proved unreliable. Spool type valves incorporating sliding seals are generally used in prior art pumps of this nature. The force necessary to move these sliding seals to actuate spool type valves are one source of the excess actuating force requiring the above mentioned large and heavy floats. In addition, spool type valves result in high maintenance and repair costs due to their tendency to freeze or to leak. There are a number of causes of the difficulties with sliding seals. These include debris entering the seals from the source of compressed air; contamination of the seals from the liquid being pumped (especially where highly corrosive waste products are pumped); loss of lubrication in the seals; and compression set of the elastomeric seals if they remain inactive for an extended period of time. In addition, some prior art pumps employ valves which have a significant cross over point where air supply is partially open and air exhaust is partially closed. At this point, the pump will tend to use a large amount of compressed air in an effort to switch to a fully open or a fully closed position. In some cases, the pump may reach a steady state condition with the head pressure in the surrounding well causing the pump to remain in a cross over, or all ports open, position.
Another difficulty with sliding seals results from their use to provide a detent action between the discharge and refill cycles of the valve. As the sliding seals wear, the ability of these sliding seals to provide a detent action will be lost. The sliding seals are normally comprised of O-rings and the wear of these O-rings will result in short and erratic pump cycles unless the O-rings are replaced. Thus, it would be desirable to provide an underground pumping system which overcomes some or all of the above mentioned difficulties.
Accordingly, it is an object of the present invention to provide a simple and inexpensive pumping system for installing in small diameter wells. It is a further object of the present invention to provide such a pumping system which is reliable, has a limited number of moving parts and which provides automatic on/off level control to eliminate the need for external controllers.
It is an additional object of the present invention to provide an underground pumping system which uses a pneumatic valve that avoids the use of sliding seals and which is switched between pumping and discharge cycles with a minimum of actuation force and without experiencing cross over. It is a further object for the present invention to provide such a pumping system having a reliable and durable detent between pump discharge and refill cycles.